CN113166575A

CN113166575A - Enhanced PVOH-based barrier layer compositions, barrier layers, and methods of making the same

Info

Publication number: CN113166575A
Application number: CN201980077332.0A
Authority: CN
Inventors: 阿里·纳德利
Original assignee: Billerudkorsnas AB
Current assignee: Billerudkorsnas AB
Priority date: 2018-11-27
Filing date: 2019-11-27
Publication date: 2021-07-23
Anticipated expiration: 2039-11-27
Also published as: CN113166575B; US20220009212A1; EP3887445A1; US20220009684A1; WO2020109401A1; CN113166512A; CN113166512B; EP3887466A1; EP3887466B1; WO2020109403A1

Abstract

A packaging material is provided comprising a fiber based substrate and a polyvinyl alcohol (PVOH) -based gas barrier layer, wherein the gas barrier layer comprises an interpolymer complex forming agent (IPCFA), the IPCFA being a water-soluble polymer exhibiting functional groups capable of forming hydrogen bonds with-OH groups of the PVOH. The PVOH has a weight average molecular weight (M) measured according to ASTM D4001-13_w) In the range of about 80kg/mol to 135kg/mol of the IPCFA and PVOH in the gas barrier layerIn a ratio in the range of 0.5 to 7.0% (w/w), and said packaging material having an Oxygen Permeability (OP) of less than 14ml μm/m²Day atm, said OP being obtained by multiplying the Oxygen Transmission Rate (OTR) of said packaging material measured according to ASTM F1927-7 at 80% Relative Humidity (RH) and 23 ℃ by the thickness of said gas barrier layer.

Description

Enhanced PVOH-based barrier layer compositions, barrier layers, and methods of making the same

Technical Field

The present disclosure relates to the field of packaging materials, and in particular to a reinforced PVOH-based barrier layer and a method of making the same, as well as packaging materials comprising the barrier layer and packages made therefrom, in particular packages for sensitive products such as, but not limited to, food, beverages, and pharmaceuticals.

Background

The packaging manufacturing industry faces a significant challenge in developing concepts that enable the production of packaging based on sustainable resources, and that can be produced at lower cost and/or energy consumption levels than is currently possible. This relates in particular to those industry panels that produce packaging for sensitive products such as food, beverages and pharmaceuticals.

Currently, these packaging products contain several layers of fossil-based polymers such as polyethylene and aluminum, which protect sensitive contents from odors, moisture, oxygen, and light under various environmental conditions (e.g., humidity and temperature). It is worth noting that even though aluminum constitutes the smallest barrier component in a packaged product, aluminum accounts for a large portion of the energy consumed in the manufacturing process of the package. Efforts to replace these materials are ongoing, but not without challenges.

Polyvinyl alcohol (PVOH) is a non-ionic water-soluble polymer that has attractive properties such as biodegradability and the ability to form an effective barrier to greases and oils, including mineral oils. Furthermore, hydrogen bonding between the hydroxyl groups of the polymer chain, together with the semi-crystalline structure of the polymer, enables the formation of a dense layer, which makes PVOH one of the best available polymer-based gas barriers. Finally, PVOH is an approved material for food packaging according to official regulations, such as those promulgated by the German Federal RirRisikobewertung, or the U.S. Food and Drug Administration (FDA); therefore, PVOH is an attractive material for the packaging industry.

WO 2013/064500(Johan Larsson and Anders Karlsson) discloses curtain coatable gas barrier coating compositions comprising a polymer and a surfactant, wherein the polymer is selected from the group consisting of polyvinyl alcohol and polysaccharides or mixtures thereof, wherein the polysaccharides are soluble or dispersible or suspendable in water, and the surfactant is a water soluble non-ionic ethoxylated alcohol. WO 2013/064500 also relates to a method for providing a substrate with a gas barrier layer by means of a coating composition, and a coated substrate having at least one gas barrier layer obtained by coating the substrate with a coating composition. Furthermore, WO 2013/064500 relates to a packaging material comprising a coated paperboard coated with a coating composition, and a liquid package comprising such a packaging material.

However, a major obstacle to the more widespread implementation of PVOH as an effective barrier in the packaging industry is the hydrophilicity of the polymer, which greatly reduces the effectiveness of the barrier under high humidity conditions. The term "high humidity conditions" herein refers to a Relative Humidity (RH) of > 50% or even > 80% RH.

There are different approaches to address this drawback. For example, attempts have been made to improve the barrier properties of PVOH films by adding nanofillers. Nanofillers are particles characterized by high surface area and high aspect ratio. High surface area and aspect ratio are advantageous in barrier applications because the particles, when optimally applied, make it more difficult for gas molecules to diffuse through the coating. However, optimal application (uniform distribution) of the nanofiller particles in the polymer matrix is difficult to achieve by industrially relevant, i.e. simple and affordable processes.

This can be explained by the high aspect ratio and surface area of the nanofiller resulting in severe agglomeration of the nanoparticles. Therefore, an excess of nanofiller, such as > 10% (w/w) based on the amount of polymer matrix, has to be used to achieve attractive gas barrier properties. This disadvantage can cause problems because the stress points created by the accumulation of the nanofillers can lead to a deterioration of the mechanical properties of the nanocomposite.

Another way to improve the barrier properties of PVOH under humid conditions is to crosslink the PVOH polymer chains. This is typically achieved by mixing the PVOH with a cross-linker before applying the formulation to a substrate or substrates and subsequently drying. However, as will be evident from the following reference, this process often involves the use of chemicals or processes that are not preferred for use in the pulp and paper industry. More importantly, the improvement achieved by this approach does not seem to be significant.

It has been indicated (see labuschgne et al, 2008) that the gas barrier properties of PVOH can be improved by densification of the amorphous portions of the semi-crystalline PVOH layer. Densification of the amorphous portion of the PVOH layer can be achieved by an interpolymer compounding process. This is achieved by adding a polymer that can strongly interact with PVOH through strong hydrogen bonding interactions. Labuschgane et al reported that barrier properties were improved by a factor of three upon addition of 20% (w/w) poly (methyl vinyl ether co-maleic acid) to PVOH.

WO 2004/089624(a.j.kruger and p.a.truter) relates to the use of interpolymer compounding concepts. In this application, the inventors illustrate their invention in terms of a formulation consisting of 30% (w/w) poly (methyl vinyl ether co-maleic acid) and 70% (w/w) PVOH on a dry weight basis. It is noteworthy that the barrier properties are only improved by a factor of three for a 25 μm barrier layer based on the formulation, which is not an excellent achievement.

In a more recent study (Lim et al, 2016), the oxygen barrier and water resistance properties of poly (vinyl alcohol) blended with poly (acrylic acid) for packaging applications were studied. Here, PVOH was crosslinked using polyacrylic acid by an esterification process, which required drying the coating at 150 ℃ for one hour. The authors report an approximately three-fold increase in barrier properties when measured at 0% RH.

There remains a need to make available PVOH-based barrier layers that perform well under high humidity conditions, i.e., 50% RH and higher, and that can be produced by processes suitable for industrial applications.

Disclosure of Invention

The present disclosure aims to solve the problems of the prior art and to obtain an improved method for forming a PVOH-based barrier layer, a PVOH-based barrier layer exhibiting excellent properties, a packaging material comprising said layer and a packaged product, i.e. a package, and in particular a package for sensitive products such as food, beverages and pharmaceuticals.

According to a first aspect, the present disclosure obtains a packaging material comprising a fiber based substrate and a polyvinyl alcohol (PVOH) -based gas barrier layer, wherein the gas barrier layer comprises an interpolymer complex forming agent (IPCFA), the IPCFA being a water-soluble polymer exhibiting functional groups capable of forming hydrogen bonds with-OH groups of PVOH, characterized in that the ratio of IPCFA to PVOH in the gas barrier layer is in the range of 0.5 to 7.0% (w/w) and the packaging material has an Oxygen Permeability (OP) of less than 14ml μ ι η/m²Day atm, said OP being obtained by multiplying the Oxygen Transmission Rate (OTR) of the packaging material by the thickness of the gas barrier layer. OTR is measured according to ASTM F1927-07 at 80% Relative Humidity (RH) and a temperature of 23 ℃. Alternatively, it may be measured according to ASTM D3985.

The thickness of the gas barrier layer is preferably obtained by dividing the coating weight of the gas barrier layer by the density of the gas barrier layer. In one embodiment, the density of the gas barrier layer is assumed to be 1.30g/cm³. Such a presumption may be particularly applicable when the gas barrier layer contains substantially no nanofillers.

Notably, PVOH-based barriers are primarily gas barriers, but to some extent also barriers for vapors and liquids.

Relatively low concentrations of IPCFA in PVOH generally reduce cost and are environmentally beneficial (e.g., degradability and/or recyclability). Furthermore, lower amounts of IPCFA generally result in fewer migration problems.

The fibre-based substrate is typically based on cellulose fibres or cellulose fibrils. The fibres or fibrils are preferably derived from wood.

According to an embodiment of said first aspect, said IPCFA has a weight average molecular weight (M)_w) In the range of 10kg/mol to 1500kg/mol, such as 25kg/mol to 1500kg/mol or 10kg/mol to 1000kg/molPreferably between 30kg/mol and 700kg/mol, more preferably between 50kg/mol and 500kg/mol, and most preferably between 100kg/mol and 700kg/mol, such as between 200kg/mol and 700 kg/mol. As shown in FIG. 2, these M_wIPCFA in the range has an optimum concentration in PVOH in the range 1-5%.

According to embodiments of the first aspect, freely combinable with the above aspects and embodiments thereof, the IPCFA is neither a cellulose or cellulose-based polymer nor a polymer comprising optionally substituted styrene groups. Cellulose or cellulose-based polymers may be too stiff to be tightly complexed with PVOH. Similarly, styrene groups can interfere with hydrogen bonding with PVOH.

The IPCFA is preferably a linear polymer, such as a linear homopolymer. The IPCFA may be non-ionic.

According to embodiments of the first aspect, freely combinable with the above aspects and embodiments thereof, the repeating unit of the IPCFA comprises an amide group, a carboxyl group or a pyrrolidone group.

According to a preferred embodiment, the IPCFA is thus a linear polymer comprising a repeating unit comprising an amide group, a carboxyl group or a pyrrolidone group, with the proviso that the linear polymer is not cellulose-based and does not comprise a repeating unit with an optionally substituted styrene group.

For example, the IPCFA may be selected from the group consisting of: polyacrylic acid, polyvinylpyrrolidone, poly (methyl vinyl ether-alt-maleic acid), and nonionic polyacrylamide. The group may be limited to polyacrylic acid, polyvinylpyrrolidone, and non-ionic polyacrylamide.

According to a further embodiment of the first aspect, freely combinable with the above aspects and embodiments thereof, the ratio of IPCFA compared to PVOH in the gas barrier layer is between 0.5-6%, 1-6% (w/w), such as 1-5% (w/w), preferably between 1-4% (w/w), more preferably between 2-3% (w/w).

According to another embodiment of said first aspect, freely combinable with the above aspects and embodiments, the PVOH has a weight average molecular weight (M)_w) In the range of 10kg/mol to 500kg/mol, preferably 50kg/mol to 300kg/mol, and more preferably about 80 to 200kg/mol, and most preferably 80kg/mol to 135 kg/mol. The advantage is that an important improvement of the oxygen barrier properties is already obtained at relatively low concentrations of IPCFA.

According to another embodiment of the first aspect, freely combinable with the above aspects and embodiments, the PVOH has a degree of hydrolysis of 98 to 100%.

According to yet another embodiment of the first aspect, freely combinable with the above aspects and embodiments, the gas barrier layer further comprises a nanofiller, preferably a nanofiller selected from the group consisting of: bentonite, kaolin, montmorillonite and mica.

According to embodiments thereof, the nanofiller is present at between about 1 to about 50 wt%, preferably about 5 to about 30 wt%, and more preferably about 10 to about 20 wt%, based on the weight of the polymer.

The oxygen barrier layer may also be substantially free of nanofillers.

According to a further embodiment of said first aspect, freely combinable with the above aspects and embodiments, the coating weight of the gas barrier layer is between 0.8 and 8.0g/m²Preferably 1.2 to 4.0g/m²And more preferably 1.6 to 3.2g/m²In the meantime.

According to yet another embodiment of the first aspect, freely combinable with the above aspects and embodiments, the fiber based substrate is a paper or paperboard comprising at least one fiber based layer. The grammage of the paper or board may be, for example, in the range of 25-400g/m²In a range of (measured according to ISO 536: 2012). In one embodiment, the substrate has a grammage of 25 to 140g/m²(ISO 536: 2012). In another embodiment, the substrate has a grammage of 140-²(ISO 536: 2012).

According to yet another embodiment of the first aspect freely combinable with the above aspects and embodiments, the gas barrier layer has an Oxygen Transmission Rate (OTR) of 0.1 to 3ml/m measured according to ASTM F1927-07 at 50% Relative Humidity (RH) and 23 ℃²Between day atm, preferably 0.1 to 2.5ml/m²Day atm, and most preferably 0.1 to 1ml/m²Between day atm.

According to yet another embodiment of the first aspect freely combinable with the above aspects and embodiments, the gas barrier layer has an Oxygen Transmission Rate (OTR) of 0.5 to 3ml/m measured according to ASTM F1927-07 at 80% Relative Humidity (RH) and 23 ℃²Between day atm, preferably 0.5 to 2.5ml/m²Day atm, and most preferably 0.5 to 1ml/m²Between day atm.

According to a second aspect, the present disclosure obtains a method for producing a packaging material according to the first aspect, wherein a coating composition comprising the PVOH and the IPCFA dissolved in a first solvent is provided, and the coating composition is applied to the substrate to form the PVOH-based gas barrier layer. The embodiments of the first aspect discussed above apply mutatis mutandis to the second aspect.

According to an embodiment of the second aspect, the forming of the PVOH-based gas barrier layer comprises drying the applied coating composition at a temperature below the boiling point of the first solvent.

According to another embodiment of the second aspect, which may be freely combined with the above, the PVOH-based layer (VOH-based layer) is crosslinked by contacting it with a crosslinking agent and optionally a catalyst after it has dried, thereby effecting crosslinking of the polymer. Crosslinking after drying has a better effect on the barrier properties than crosslinking before drying.

After contact with the crosslinking agent, the PVOH substrate is typically dried again at a temperature below the boiling point of the solvent in which the crosslinking is applied. After such drying, the PVOH substrate may undergo a heating step, typically to a temperature of between 101-170 ℃, preferably between 130 and 160 ℃, and most preferably between 140 and 150 ℃. Thus, a curing effect can be obtained.

According to a further embodiment of the second aspect, the coating composition may be applied to the fiber based substrate by curtain coating, knife coating, bar coating, spray coating or roll coating or a combination of two or more thereof, freely combinable with the above aspects and embodiments.

A third aspect of the present disclosure is a package or container comprising the packaging material according to the first aspect or one or more embodiments thereof. The packaging is preferably a packaging for an edible product, food, beverage or medicament.

Other aspects and embodiments thereof will be apparent to the skilled person after studying the following claims and description, including the drawings and examples.

Drawings

Fig. 1 shows, from left to right, the interpolymer complex forming polymers tested in the examples: chemical structures of polyvinyl alcohol, nonionic polyacrylamide, poly (methyl vinyl ether-alt-maleic acid), polyacrylic acid, and polyvinylpyrrolidone.

Fig. 2 shows the polymer composition for four different interpolymer complex forming polymers: estimated optimal concentration (% w/w) in PVOH-IPCFA blends determined by polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), poly (methyl vinyl ether-alt-maleic acid) (PMV), and non-ionic polyacrylamide (NPA). X-axis of FIG. 2 represents M_w。

Fig. 3 shows the change in shear viscosity with the concentration of PVP of different weight average molecular weights in different PVOH qualities:

in FIG. 3A, the PVOH quality is POVAL 6/98 (M)_w＝47kg/mol)；

In FIG. 3B, the PVOH quality is Mowiol 10/98 (M)_w＝61kg/mol)；

In FIG. 3C, the PVOH quality is POVAL 15/99 (estimate M)_w＝100kg/mol)；

In FIG. 3D, the PVOH quality is Mowiol 20/98 (M)_w＝125kg/mol)；

In FIG. 3E, the PVOH quality is POVAL 15/99 (M)_w145 kg/mol); and

in FIG. 3F, PVOH quality is 363146(Sigma Aldrich) (M)_w85-124 kg/mol). Fig. 3F also includes PAA.

FIG. 3G shows a reference experiment with Exceval AQ4104, Exceval AQ4104 having similar characteristics to the estimated M_wEVOH of 70kg/mol and M contained therein_wModified PVOH at 360kg/mol PVP.

Figures 4a and b show the pinhole test results for paperboard substrates coated with the experimental coating formulations: a) pure PVOH; b) PVOH containing 10% (w/w) nanofiller; c) PVOH-PMV (2.5% (w/w)); d) PVOH-PMV (2.5% (w/w)) 10% nanofiller; e) PVOH-PAA (1% (w/w)); f) PVOH-PAA (1% (w/w)) 10% (w/w) nanofiller; g) PVOH-PVV (2.5% (w/w)); and h) PVOH-NPA (2% (w/w)).

FIG. 5A shows the following PMV (M)_w216kg/mol) viscosity as a function of concentration in PVOH (POVAL 15/99) (open squares/dashed line) and OTR at 80% RH and 23 ℃ (solid squares/solid line).

FIG. 5B shows PVP (M) with PVP_w360kg/mol) viscosity as a function of concentration in PVOH (POVAL 15/99) (open triangles/dashed line) and OTR at 80% RH and 23 ℃ (closed triangles/solid line).

FIG. 5C shows the tracking of PAA (M)_w250kg/mol) viscosity as a function of concentration in PVOH (POVAL 15/99) (open star/dashed line) and OTR at 80% RH and 23 ℃ (solid star/solid line).

Detailed Description

The term "substrate" refers to any substrate on which it is desirable to improve barrier properties and to which a PVOH-based coating can be applied. The present disclosure relates generally to cellulose and/or fiber-based substrates, such as films or papers, including paperboard made of or containing cellulose fibers and/or cellulose fibrils.

The term "fiber" encompasses cellulosic fibers such as virgin fiber (virgin fiber), e.g. bleached and/or unbleached kraft pulp or chemi-thermo-mechanical pulp (CTMP), but also recycled fiber, pulp recycled paper, such as pulp newsprint, deinked pulp (DIP), etc.

"molecular weight" generally refers to the weight average molecular weight (M)_w) It can be determined according to the standard ASTM D4001-13.

According to a first aspect, there is provided a gas barrier comprising a fibre-based substrate and a polyvinyl alcohol (PVOH) -based gas barrier layerA packaging material, wherein the gas barrier layer comprises an interpolymer complex forming agent (IPCFA), the IPCFA being a water-soluble polymer exhibiting functional groups capable of forming hydrogen bonds with-OH groups of PVOH. The ratio of IPCFA to PVOH in the gas barrier layer is in the range of 0.5 to 7.0% (w/w) and the packaging material has an Oxygen Permeability (OP) below 14ml μm/m²Day atm, said OP being obtained by multiplying the Oxygen Transmission Rate (OTR) of the packaging material measured according to ASTM F1927-07 at a Relative Humidity (RH) of 80% by the thickness of the gas barrier layer.

The barrier layer inhibits the migration of gases and to some extent also of vapors and liquids.

The ratio of IPCFA compared to PVOH in the barrier layer may be between 1-5% (w/w), preferably between 2 and 3% (w/w). This is an unexpectedly small amount, particularly when compared to previous disclosures teaching the addition of about 30% of a polymer forming an interpolymer complex.

The PVOH preferably has a degree of hydrolysis of at least about 98%, or between about 98 and 100%. Furthermore, it is preferred to use fully saponified grades of PVOH. Different qualities of PVOH having a degree of hydrolysis of about 98-100% are available, for example having the following M_wThe product of (a): 13-23kg/mol, 27kg/mol, 31-50kg/mol, 89-98kg/mol, 85-124kg/mol, 125kg/mol, 130kg/mol, 145kg/mol, 146-186kg/mol and 195 kg/mol.

Again without wishing to be bound by theory, the inventors have found that the molecular weight of PVOH, as well as the molecular weight of IPCFA and combinations thereof, are of significant importance. The advantageous molecular weights of PVOH and IPCFA are discussed above.

PVOH products are often characterized by a 4% solution viscosity. The skilled person is very familiar with different standard methods for determining the viscosity of polymers, for example using capillary-type viscometers, such as Ubbelohde-type viscometers or Ostwald-type viscometers. Notably, PVOH products having viscosities above 5mPas have been approved by FDA/BfR.

Thus, according to another embodiment of said first aspect, freely combinable with the above aspects and embodiments, the viscosity of PVOH is preferably between about 4 to 28mPas, preferably above 5mPas, as determined according to standard DIN 53015/JIS K6726 at 20 ℃, since PVOH products having a viscosity above 5mPas have been approved for FDA/BfR for food packaging applications.

The experimental results presented below show that the combined use of IPCFA and nanofiller not only makes it possible to reduce the amount of both components, but also may have a positive effect on the reduction of the formation of pinhole defects (see fig. 4). It is possible to reduce the amount of nanofiller by including IPCFA: s in the composition, which is advantageous also because it reduces the risk of the barrier layer becoming brittle, a property sometimes associated with nanoparticles.

The possibility of combining IPCFA: s and a reduced amount of nanofiller is desirable in some applications, when a barrier layer without nanofillers is desired for most applications. When coating three-dimensional objects or substrates that are required to be flexible in subsequent packaging applications, it would be a considerable advantage that the amount of nanofillers can be minimized or avoided altogether in filling, closing or other processing steps where flexibility and durability of the barrier layer are important.

The coating weight of the barrier layer is usually from 0.8 to 8.0g/m²Preferably 1.2 to 4.0g/m²And more preferably 1.6 to 3.2g/m²In the meantime.

The substrate is a fiber based substrate such as paper or paperboard comprising at least one fiber based layer.

A second aspect of the present disclosure relates to a method for producing a packaging material according to the first aspect, wherein a coating composition comprising the PVOH and the IPCFA dissolved in a first solvent is provided and the coating composition is applied to the substrate to form the PVOH-based gas barrier layer.

The coating composition may be applied to a substrate by curtain coating, knife coating, bar coating, spray coating, or roll coating, or a combination of two or more thereof.

Those skilled in the relevant art are familiar with techniques for coating substrates, particularly fiber-based substrates such as paperboard. Curtain coating is a coating process in which a linear stream of a liquid coating composition is deposited on the surface of a moving substrate, such as a paper web. The coating composition forms a liquid film (liquid sheet) that falls freely before impinging on the moving substrate to be coated.

The forming of the PVOH-based gas barrier layer may include drying the applied coating composition at a temperature below the boiling point of the first solvent. Examples of drying methods are air drying using hot air, xenon flash lamp heating, UV radiation, IR radiation, microwave based drying and convection heating.

Crosslinking of the polymer can be achieved by contacting the PVOH substrate with a crosslinking agent (and optionally a catalyst) to crosslink it after it has dried. Crosslinking after drying has a better effect on the barrier properties than crosslinking before drying.

After contact with the crosslinking agent, the PVOH substrate is typically dried again at a temperature below the boiling point of the solvent in which the crosslinking is applied. Examples of drying methods are discussed above. After such drying, the PVOH substrate may be subjected to a second heating step, typically to a temperature of between 101-170 ℃, preferably between 130 and 160 ℃, and most preferably between about 140 and about 150 ℃. This heating may be performed for 1 to 10 seconds or 1 to 3 minutes. Different heating methods may be employed, such as hot air heating, xenon flash lamp heating, UV radiation based heating, IR radiation based heating, microwave based heating, or convection heating.

The process has proven to be very reliable and for example the inventors have shown that coating compositions and cross-linking compositions can be prepared in tap water, which constitutes an advantage when the process is applied on an industrial scale.

A third aspect of the present disclosure is a package or container comprising the packaging material according to the first aspect. The packaging is preferably a packaging for an edible product, food, beverage or medicament.

Examples

The inventors have carried out a great deal of experimental work using unmodified PVOH layers as reference to obtain improved barrier properties at high relative humidity.

Material

PET plastic films were used as substrates in the bar coating experiments. Duplex 370 carton board (

AB, sweden) was used as substrate (brown side of coated panel) in the curtain coating experiment.

KURARAY

15-99(Kuraray America) were used as PVOH in the experiments presented in Table 1 below and FIGS. 2-5. This polymer has a degree of hydrolysis of 99% and a viscosity of 12.5-17.5 mPa.s (measured at 4% (w/w)), estimated M_wAbout 100 kg/mol. The following PVOH was also used in the experiment presented in fig. 3:

-POVAL 6/98，M_w47kg/mol (viscosity at 4% (w/w) ═ 4-5 mPas);

-Mowiol 10/98，M_w61kg/mol (viscosity at 4% (w/w) ═ 9-11 mPas);

-Mowiol 20/98，M_w125kg/mol (viscosity at 4% (w/w) 9-11 mPas);

-Poval 28/99，M_w145kg/mol (viscosity at 4% (w/w) 26-30 mPas); and

poly (vinyl alcohol), Sigma Aldrich product number 363146M_w＝85-124kg/mol。

In the reference experiment presented in fig. 3G, Exceval AQ4104(kuraray) was used, which is the estimated M with_wEVOH a quality of 70 kg/mol.

The other components are as follows:

-

(Southern Clay Products/BYK Additives&instruments) that are micronized nanofillers; and

-

ON70(BASF/BTC Europe GmbH)，it is a fatty alcohol ethoxylate.

Interpolymer (b):

-nonionic polyacrylamide from Sigma Aldrich, having M_nAbout 40kg/mol (NPA)_{Is low in}) And 150kg/mol (NPA)_{Height of}) M corresponding to about 74kg/mol and 400kg/mol, respectively_w。

Poly (methyl vinyl ether-alt-maleic acid) with M friendly supplied by Ashland Global Specialty Chemicals, inc_nAbout 960kg/mol (PMV)_{Height of}) And 80kg/mol (PMV)_{Is low in}) Corresponding to M of about 1980kg/mol and 216kg/mol, respectively_w。

Polyacrylic acids having M_wAbout 250kg/mol (PAA)_{Is low in}) And about 1300kg/mol (PAA)_{Height of}) (ii) a And

polyvinylpyrrolidone having M_w29kg/mol (PVP)_{Is low in})、360kg/mol(PVP_m) And 1300kg/mol (PVP)_{Height of}). In addition, has M_wPVP at 55kg/mol was included in the experiment presented in fig. 3C.

Tap water was used in all experiments.

Method

1. Preparation of Polymer solutions on a laboratory Scale (for rheology Studies)

PVOH-PMV, PVOH-PAA and PVOH-PVP solutions were prepared by adding the polymer to water at room temperature with continuous stirring, followed by heating at 95 ℃ for one hour.

The PVOH-NPA solution was prepared by first preparing stock solutions of the different polymers. PVOH (about 9% (w/w)) was prepared by mixing at 95 ℃ for one hour, and NPA stock solution (1% (w/w)) was prepared by continuous stirring at room temperature overnight. NPA was added to the PVOH solution at 60 ℃ with stirring. The system was then removed from the heater and stirred for an additional ten minutes.

2. Preparation of Polymer solutions on a laboratory Scale (for Barrier Studies)

Polymer blends were prepared using a similar protocol to that in the previous sectionA compound (I) is provided. However, the use of nanofillers

In the study of (1), the nanofiller was first dispersed in water within ten minutes, followed by addition of the polymer and then heating. At 40 ℃ will

NO70 (0.4% (w/w)) was added to the polymer blend.

3. Preparation of Polymer solutions on a semi-pilot scale (for Barrier Studies)

An industrial boiling pot with a capacity of 50 liters was used. The preparation of the different polymer blends was carried out in a similar manner to that described above.

The amount of NO70 was 0.4% w/w in the curtain coating formulation. Not investigated for each polymer blend

The optimum amount of (a).

4. Coating substrates with PVOH-based formulations

In laboratory scale experiments, the polymeric solution was applied to the plastic substrate by a laboratory bar coater. The coating is subsequently dried by IR.

In a semi pilot scale setup, coating was performed using a lab scale curtain coater. The conveying speed was about 6.5m/s and the pumping rate was about 3 l/min. The resulting coated substrate was dried in a laboratory oven at 60 ℃ for 20 min.

5. Rheology study

The shear viscosity of the polymer suspension was measured at 25 ℃ using a rheometer (TA Instruments ltd., Delaware, usa) with a cup-hammer geometry (smooth surface). The viscosity is measured in the range of 10-1000 s^-1Within the range of (1).

6. Barrier properties

OTR (measured at 80% RH/23 ℃) of the coated film Using ASTM F1927-07 from Mocon corporation

The instrument performs the measurement. The Oxygen Permeability (OP) of the different systems was calculated by normalizing the measured OTR values with the thickness of the coating. Initial thickness values were obtained by SEM measurements. For SEM measurements, the samples were molded in epoxy to penetrate the pore system of the material to encase the membrane. The sample was then cut to expose a fresh surface, and the surface was then polished using a series of successively finer grade diamond pastes. The cross-section was then analyzed by SEM.

8. Assessment of pinholes

Coating of Duplex 370 carton boards with experimental compositions for curtain coating (

AB, sweden). Pinhole testing was performed according to the INS-06271-v.2.0 protocol.

Results

The optimum composition of PVOH and the different IPCFA: s was determined by rheological studies. The optimal concentrations of the different polymers are presented in FIG. 2, which includes IPCFA PVP_m、PVP_{Height of}、PAA_{Is low in}、PMV_{Height of}、PMV_{Is low in}、NPA_{Is low in}And NPA_{Height of}. FIG. 2 shows M having_wLow optimum concentration of IPCFA lower than 1980kg/mol but higher than 74kg/mol, and in particular with M_wLow optimum concentration of IPCFA of 1300 kg/mol.

10s as a function of PVP molecular weight and concentration in different PVOH qualities^-1The shear viscosity of (A) is shown in FIGS. 3A-F. FIG. 3F also includes PAA_{Is low in}. Notably, only M with can be observed_wAn optimum concentration of PVOH quality above 61kg/mol but below 145 kg/mol. For having an estimate M_wEVOH-like quality of 70kg/mol, and PVP was not observed in the range of 0 to 10%_mOptimum concentration of (see)Fig. 3G).

Figure 5 shows that at the same IPCFA concentration as the viscosity peak, the OTR reaches the optimum (nadir). Therefore, conclusions about the oxygen barrier properties can be drawn from fig. 3.

Table 1 presents the OTR of the coated films prepared in the laboratory scale experiments by bar coating, and of the coated carton boards prepared in the semi pilot scale by curtain coating. IPCFA was used at the following concentrations based on optimization: PMV about 2.5% (w/w), NPA about 2% (w/w), PAA about 1% (w/w) and PVP about 2.5% (w/w). OTR_StickAnd OTR_ScreenA similar trend is shown, i.e. the barrier properties are improved by including a small amount of IPCFA. In many experiments the pH was adjusted and the pH values indicated with an "x" are the actual pH of the system without pH adjustment.

²TABLE 1 OTR (ml/m day atm) of the coated films (at 23 ℃ C.)

d means the thickness (μm) of the PVOH-based gas barrier layer as measured by SEM

^§Estimated value based on the amount administered

In evaluating the results, it should also be borne in mind that the coating thickness (as measured by SEM) is about 1-2 μm. It should also be emphasized that the experimental method has not been fully optimized and that the properties of the barrier layer are determined when testing the layer alone, rather than using a sandwich structure as used in the packaging industry. Depending on the requirements of a particular package, various barrier layers may be combined, for example a layer with good moisture barrier properties may be used to protect a layer with good oxygen barrier properties but with less moisture resistance. However, although the object of the present disclosure is to obtain barrier layers with improved oxygen barrier properties also under high humidity conditions, these layers can of course be used in combination with other layers.

The results show that highly desirable barrier properties, especially at high relative humidity, can be obtained by a process well suited for industrial applications. In addition, the use of nanofiller and interpolymer complexing agents can be minimized. It is also possible to produce barrier layers that do not require covering with additional protective layers as required in many competing processes.

Reference to the literature

WO 2004/089624–Packaging；Arnoldus J.Kruger and Patricia A.Truter

WO 2013/064500-Coating composition,a method for coating a substrate,a coated substrate,a packaging material and a liquid packaging；Johan Larsson and Anders Karlsson

Labuschagne PW,Germishuizen WA,C.Verryn SM,Moolman FS(2008),Improved oxygen barrier performance of poly(vinyl alcohol)films through hydrogen bond complex with poly(methyl vinyl ether-co-maleic acid),European Polymer Journal 44:2146-2152

doi:https://doi.org/10.1016/j.eurpolymj.2008.04.015

Lim M,Kim D,Seo J(2016),Enhanced oxygen-barrier and water-resistance properties of poly(vinyl alcohol)blended with poly(acrylic acid)for packaging applications,Polymer International 65:400-406 doi:10.1002/pi.5068。

Claims

1. A packaging material comprising a fiber based substrate and a polyvinyl alcohol (PVOH) -based gas barrier layer, wherein the gas barrier layer comprises an interpolymer complex forming agent (IPCFA), the IPCFA being a water-soluble polymer exhibiting functional groups capable of forming hydrogen bonds with-OH groups of the PVOH, characterized in that the PVOH has a weight average molecular weight (M) measured according to ASTM D4001-13_w) In the range of 80 to 135kg/mol, the ratio of IPCFA to PVOH in the gas barrier layer is in the range of 0.5 to 7.0% (w/w), and the packaging material has an Oxygen Permeability (OP) of less than 14ml μm/m²Day atm, said OP being obtained by multiplying the Oxygen Transmission Rate (OTR) of said packaging material measured according to ASTM F1927-7 at 80% Relative Humidity (RH) and 23 ℃ by the thickness of said gas barrier layer.

2. The packaging material of claim 1, wherein the IPCFA has a weight average molecular weight (M)_w) Between 10kg/mol and 1500kg/mol such as 25kg/mol and 1500kg/mol or 10kg/mol and 1000kg/mol, preferably between 30kg/mol and 700kg/mol, more preferably between 50kg/mol and 500kg/mol, and most preferably between 100kg/mol and 700kg/mol such as 200kg/mol and 700 kg/mol.

3. The packaging material according to claim 1 or 2, wherein the IPCFA is selected from polyacrylic acid, polyvinylpyrrolidone and non-ionic polyacrylamide.

4. The packaging material according to any one of the preceding claims, wherein the ratio of IPCFA to PVOH in the coating composition is between 0.5 to 6% (w/w), such as 1 to 5% (w/w), such as 1 to 4% (w/w).

5. A packaging material according to any one of the preceding claims, wherein the fibre-based substrate is paper or paperboard comprising at least one fibre-based layer.

6. The packaging material according to any one of the preceding claims, wherein the packaging material has an Oxygen Transmission Rate (OTR) of from 0.1 to 3ml/m, measured according to astm f1927-07 and at a Relative Humidity (RH) of 50% and 23 ℃²Between day atm.

7. The packaging material according to any one of the preceding claims, wherein the packaging material has an Oxygen Transmission Rate (OTR) of from 0.5 to 3ml/m, measured according to astm f1927-07 and at a Relative Humidity (RH) of 80% and 23 ℃²Between day atm.

8. A method for producing the packaging material according to any of claims 1 to 7, wherein a coating composition comprising the PVOH and the IPCFA dissolved in a first solvent is provided, and the coating composition is applied to the substrate to form the PVOH-based gas barrier layer.

9. The method of claim 8, wherein the forming of the PVOH-based gas barrier layer comprises drying the applied coating composition at a temperature below a boiling point of the first solvent.

10. The method according to claim 8 or 9, wherein the forming of the PVOH-based gas barrier layer comprises drying the applied coating composition and heating the dried coating composition.

11. The method according to any of claims 8 to 10, wherein crosslinking of the polymer is achieved by crosslinking the PVOH base layer by contacting it with a crosslinking agent after the PVOH base layer has been dried and optionally heated.